1. Field of the Invention
The present invention relates to low sound region reproducing speaker systems, and more particularly to such systems suitable for use in 3D reproducing systems.
2. Prior Art
A conventional known low sound region reproducing system of this type is shown, for example, in FIGS. 5 and 7.
The speaker system of FIG. 5 includes a pair of speakers 13 and 14 provided on a partition wall 12 within a single box 11 to thereby acoustically mix right and left stereophonic channel signals.
The speaker system is constructed so as to mix two low region sounds in a superposed manner as shown in FIG. 6(C) in the external space, the two low region sounds having the characteristics shown in FIGS. 6(A) and (B) emitted by two Helmholtz resonant systems having different resonant frequencies and constituted by two open ducts 15, 16 of different lengths and two spatial portions V11, V12 of different volumes (see, for example, a speaker system 501X, manufactured by BOSE Co., USA).
Since this system superposes in the external space the two low sound regions emitted by the two Helmholtz resonant systems of different resonant frequencies, as described above, its high region attenuation characteristic is excellent. However, if the ratio in resonant frequency of the two resonant systems is set to a large value in order to expand a reproduced low sound region, its attenuation characteristic will change as shown in FIG. 6(D); namely, it cannot virtually provide a flat characteristic.
The speaker system of FIG. 7 is constituted by a box 21 closed on all its sides, a partition wall 22 dividing the internal space of the box into two spatial portions V21 and V22, a pair of speakers 23 and 24 attached to the partition wall 22, and a duct 25 provided on the side wall of the box 21 for communicating the external space with one (V21) of the spatial portions V21, V22.
This speaker system is constructed such that right and left stereophonic channel signals are individually reproduced as sounds by the pair of speakers 23 and 24, the sounds are acoustically mixed within the box 21, a sound region other than a low sound region of a predetermined band width is attenuated by two resonant systems of different resonant frequencies and constituted by the two spatial portions V21 and V22 and duct 25 and the remaining low sound region is emitted into the external space (see, for example, Unexamined Japanese Patent publication No. Sho 55-52694).
The speaker system of FIG. 7 can reproduce a relatively wide band with a single aperture, but one of the spatial portions is closed, so that to reduce the reproduction limit frequency and to reproduce a low sound region having a flater characteristic and enough sound pressure are limited in connection with the volume and structure of the box.